UVEAL TRACT

NOMENCLETURE

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• Intermediate coat

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• Middle coat

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• Vascular coat

COMPOSITION

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• IRIS

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• CILIARY BODY

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• CHOROID

IRIS

• LOCATION : Lies in front of
• Crystalline lens
• Ciliary body

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• Separates :
• Anterior chamber
• Posterior chamber

• Average diameter : 12mm

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• Thickness : 0.5mm

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• It is a delicate diaphram with a central opennning called the PUPIL (3 – 4mm)

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• The pupil is suspended freely in the Anterior Segment of the eye from a peripheral attachment and the ciliary body and the LIGAMENTUM PECTINATUM

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Iri cont’d

• Thinnest at the it’s root and easily tears away on blunt trauma (iridodialysis)

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• The iris root appears as trucated cone because the pupillary margin is supported by the curved anterior surface of the lens

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• The periphery of the iris which is attached to the anterior surface of the CB is called the CILIARY MARGIN or ROOT OF THE IRIS while the pupil is surrounded by the pupillary margin and thinnest at the ciliary margin

Iris cont’d

• The colour of the iris varies from light blue to dark brown : the colour may vary from one eye to another in the same person and in different part of the iris.

Iris cont’d

MACROSCOPIC APPEARANCE

• TWO SURFACES
• Anterior surface
• Posterior surface

ANTERIOR SURFACE

• COLLARETTE:
• Zigzag line, 2mm from pupil, thickest, represents attachment of pupillary membrane.
• Divides surface into : A
• Ciliary zone
• Radial zone
• Crypts- peripheral- near the iris central-near collarette

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Macroscopic appearance cont’d

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• Contraction furrow :
• Faint lines outside collarette.

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• B : PUPILLARY ZONE

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• B/w collarette and pigment frill

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• Pigmented frill – black pigment at pupillary margin and represents end of the optic cup

B. POSTERIOR SURFACE

• The colour of this surface appears dark brown/black.

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• COMPOSITION :

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1. Schwalbe’s line contraction folds -1mm from pupillary border,, little radial furrows

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• Schwalbe’s structural furrows -1. 5mm from pupillary border.

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• Circular furrows – finer than radial furrows.

MICROSCOPIC STRUCTURE

• The iris contain 4 layers :
• ANTERIOR LIMITING MEMBRANE
• Consists of melanocytes and fibroblasts. This was previously called endothelium
• Colour of iris in this layer
• Blue iris – thin layer and few pigment cells
• Brown iris, thick and doubly pigmented.

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2. IRIS STROMA

• Forms main bulk
• Consist of collagenous tissue with mucopolysaccharide

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• MICROSCOPIC STRUCTURE CONT’D

• Structures embedded-

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• SPHINTER PUPILLAE :
• 1mm broad circular band in pupillary area derived from the ectoderm.
• Supplied by parasympathetic fibres by 3^rd nerve
• Constricts pupil.

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• DILATOR PUPILLAE :
• Lies in posterior part of the ciliary zone
• Supplied by cervical sympathetics
• Dilates the pupil

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Microscopic structure cont’d

• VESSELS ;
• Forms bulks of stroma
• Radial Vessels –branches of circulous arteriosis major.
• Pecularities –absence of IEL and non fenestrated capillary endothelium

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• Pigment cells – melanocytes

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• Lymphocytes, fibroblast and macrophages

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MICROSCOPIC STRUCTURE CONT’D

• C) ANTERIOR EPITHELIAL LAYER :
• Anterior continuation of pigment epithelium of retina and ciliary body

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• Basal processes :
• Give rise to dilator pupillae
• D) POSTERIOR PIGMENTED EPITHELIUM ;
• Anterior continuation of non pigmented epithelium of ciliary body
• Derived from internal layer of optic cup
• Forms pigmented frill

FUNCTIONS OF IRIS

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• Controls amount of light entering the eye through pupil

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• Defines eye colour

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• Control depth of focus

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• Source of blood ocular tissues

BLOOD SUPPLY

• The blood supply is provided by radial vessels in the stromal layer extend from the major arterial circle of the iris located in the ciliary body.

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NERVE SUPPLY

• The iris is richly supplied with nerves for the short ciliary and long ciliary nerves that carry sensory motor and sympathetic.

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CILIARY BODY

• Forward continuation of choroid at ora serrata
• Triangular in cut section, anterior side of it’s form part of angle in middle, attached into iris and outer part lies against sclera.
• Triangle – two parts
• Anterior part:– Ciliary processes (pars plicata) 2 – 2.5mm
• Posterior part:–Smooth (pars plane) 5mm wide temporally and 3mm nasally

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MICROSCOPIC STRUCTURE

• 1) SUPRACILIARY LAMINA (outermost part)
• Consist of pigmented collagen fibres
• Posteriorly continuation of supra choroidal lamina anterior continuous with anterior limiting membrane

2)STROMA

Consist:

• Ciliary muscle – non striated triangular in cut section 3 parts.
• Longitudinal/merilional fibre – origin for sclera spur, insert into suprachoroidal lamina
• Circular fibres – in inner portion, nearest to lens
• Radial fibres – obliquely placed

Actions – slacken suspensory ligament, this helps in accommodation

Circular fibres – directly as sphiricter

Nerve supply – parasynthetic fibres from ciliary ganglion.

• Vascular stroma – major arterial circle lies.
• Formed by anastomosis of long and short PCA
• Supplies iris and ciliary body

3. LAYER OF PIGMENTED EPITHELIUM

• Forward continuation of RPE
• Anterior continuous to pigmented epithelium of iris

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4. LAYERS OF NON PIGMENTED EPITHELIUM

• Forward continuation of sensory retina
• Continues anterior with pigmented epithelium of iris

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5. INTERNAL LIMITING MEMBRANE

• Line NPE
• Forward continuation of internal limiting membrane of retina

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CILIARY PROCESSES

• Finger like projections from pars plicata
• 70 – 80 in number, 2mm long 0.5mm diameter
• Site of aqueous production

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ULTRASTRUCTURE

1. Network of capillaries – in the centre
1. Has endothelium with fenestrae
2. Stroma of ciliary processes -
1. A thin, separates capillaries from epithelium

3. Epithelium – two layered with apical apposition

FUNCTIONS OF CILIARY BODY

• Site of AH production
• Maintenance of IOP
• Constitutes blood aqueous barrier
• Accommodation
• Eicosanoids are synthesized in ciliary

CHOROID

• Posterior 5/6 of the middle part of the globe
• Extension – optic disc to Ora serrata
• Inner surface – smooth brown and contact with RPE.
• Outer surface – rough and in contact with the sclera
• Thickness:
• Posteriorly 0.22mm
• Anteriorly 0.10mm

MICROSCOPIC STRUCTURE

1. Suprachoroidal – lamina fusca
1. Thin layer, continues anteriorly with supraciliary lamina of ciliary body
2. Suprachoroidal space – contains long and short ciliary arteries and nerves
2. Stroma – plenty of pigmented cells, macrophages, mast and plasma cells
1. Vessels – for the bulk
2. Arranged in two layers – outer consisting of large vessels (hallens layer), inner of medium vessels (sattler’s layer)

3. Choriocapillaris – rich capillary network
1. Supplies pigment epithelium and outer layers of sensory retina
2. Few anastomosis with CRA
4. Basal lamina – Bruch’s membrane / lamina vitrae
1. Innermost layer
2. Between choriocapillaries and RPE
3. Electron microscopy – basement membrane of RPE, inner collagen, middle elastic and outer collagen and basement membrane chorio-capillaries.
4. With increasing age – produces hyaline excrescences known as druscens.

FUNCTIONS OF CHOROID

• Blood supply to outer four layers of retina
• Modulation of vascularization
• Regulate retina heat
• Assist in the control of intraocular pressure
• Pigment absorbs excess light so avoiding reflection

BLOOD SUPPLY UVEAL TRACT

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• SHORT POSTERIOR CILIARY ARTERIES
• Branches of ophthalmic artery
• Divides into 10 -20 branches, pierce sclera around optic nerve
• Supply choroid in segmental manner.

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• LONG POSTERIOR CILIARY ARTERIES
• Two in No –nasal and temporal
• Pierce sclera
• Anastomose with anterior –
• Forms major arterial circle supply- ciliary body

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• ANTERIOR CILIARY ARTERIES
• From muscular arterieS
• 7 in No
• 2 each SR, IR, MR, 1 From LR
• Anaatomose with LPCA
• Circulus arteries major and minor

VENOUS DRIANAGE

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• ANTERIOR CILIARY VEIN –
• Tributaries of muscular veins

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• SMALLER VEINS FROM SCLERA
• Carry blood only from sclera and not from choroid

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• VENA VERTICOSAE
• 4 in No and drain whole of choroid